An integrated circuit chip, or die, is ordinarily formed as part of a much larger body, referred to as a wafer, and then released from the wafer by sawing. More specifically, many integrated circuit patterns are simultaneously defined or formed in a single wafer. The integrated circuit patterns are arranged in rows and columns, with the periphery of each pattern being rectangular. After the integrated circuits are fully defined, the wafer is sawed along lines between the rows and columns, which is also parallel to the edges of the patterns. By sawing completely through the wafer on those lines, the wafer is cut up into a plurality of chips, or dice. Such sawing of the wafer into individual chips or dies is referred to as dicing because the dies are also referred to as dice.
When dicing by sawing, the saw is ordinarily a rotating blade. As the saw blade rotates against the silicon wafer, it abrades the silicon away, creating colloidally small silicon particles.
The cutting area and the rotating blade are ordinarily bathed in a significant flow of deionized water. One would think that the silicon residue would be flushed away by the water coolant that floods the cutting area. Unfortunately, even under significant flooding, the small silicon particles are not completely flushed away. They adhere to the bond pads of the integrated circuit chips, leaving a silicon particle debris or residue thereon, which adversely affects the bond pads. This moist environment and the adhesion of the silicon particles is known to cause deleterious corrosion and abrasion effects. The deleterious corrosion is due, at least in part, to galvanic action of segregated copper in the aluminum alloy of the bond pad. The deleterious abrasion occurs when one scrubs the surface of the chips to remove the silicon particles from the bond pads. In some applications, these effects can be tolerated. In others, it cannot.
In the past, attempts have been made to avoid formation of the silicon residue, and its associated corrosion and/or abrasion effects. Several approaches were used. They included oxygen baking or oxygen plasma treating the wafer before sawing, or exposing the wafer to nitric acid before sawing. We have not been able to successfully use any of these treatments. In addition, they add an additional step to wafer processing prior to sawing. Another way to reduce the silicon residue effect is to mechanically scrub the wafer surface after sawing. This obviously adds an extra processing step after sawing, which is objectionable. However, there is another objection. The silicon particles are relatively hard. During the mechanical scrubbing, the silicon particles can scratch the chip bond pads. The scratched bond pads can be a cause of scrap.
On the other hand, we have found a simple solution to this problem that does not entail prior or post added processing steps. Our solution is a method that is readily integrated into existing processes and equipment.